The present invention relates to an automatic tool changing device for machining centers such as a numerical control milling machine with an automatic tool changing device.
Two principal types of such device are known in the art. They are a turret head type, and an arm type in which the required tool changes are effected by intermediary means such as an arm and a tool transport unit which are arranged between a tool magazine and the main shaft or spindle of a machine tool. A disadvantage of the former or the turret head type is that while the required tool changing time is relatively short, the number of tools that can be held on the head is usually on the order of 6 to 8 tools thus making it unsuitable for use on machining centers designed to perform a variety of machining operations and moreover there is the disadvantage of causing indexing error, misalignment and the like. The latter or the arm type is also disadvantageous in that since the head carrying a tool must first be raised to a predetermined height to permit the tool change by the intermediary means such as a robot and then the head must be lowered to effect the machining of the work, even in the case of a small-sized work the head must be raised to the predetermined height thus requiring a waste time, wasting time in changing the tools, unavoidably making the device larger and more complicated in construction and making it impossible to use this type of device on machining centers particularly in view of the recent trend in designing toward smaller machining centers.
With a view to overcoming the foregoing deficiencies, the inventor has proposed in U.S. Patent Application Ser. No. 817,529 an automatic tool changing device in which an annular channel is formed in the outer peripheral surface of a drum and a large number of arbors are movably fitted in the annular channel, whereby one of the arbors is engaged with the main shaft of a head and the remaining arbors are continuously arranged along the upper periphery of the drum above a position spaced by a predetermined angle from the engaged arbor on each side thereof. However, this device is also disadvantageous in that the rotation of the arbors for tool changing purposes can be made only by an amount corresponding to one arbor and in one direction only and thus it is impossible to move the arbors in either the counterclockwise direction or the clockwise direction as desired and thereby select the desired tool in a short period time.